Update AccountCreationAuth & fix auth.HashToSign

- Fix AccountCreationAuth.HashToSign (was using `[]byte("0x...")`, which
uses the bytes of the string. Now uses the bytearray of the compressed
BJJ public key (compatible with js implementation))
- Update AccountCreationAuth to last specification (add to hash
parameters ChainID & HermezAddress)
- Add missing test to AccountCreationAuth

common/accountcreationauths_test.go

@@ -0,0 +1,41 @@
+package common
+
+import (
+	"encoding/hex"
+	"testing"
+
+	ethCommon "github.com/ethereum/go-ethereum/common"
+	ethCrypto "github.com/ethereum/go-ethereum/crypto"
+	"github.com/iden3/go-iden3-crypto/babyjub"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestAccountCreationAuth(t *testing.T) {
+	// Ethereum key
+	ethSk, err := ethCrypto.HexToECDSA("fad9c8855b740a0b7ed4c221dbad0f33a83a49cad6b3fe8d5817ac83d38b6a19")
+	require.NoError(t, err)
+	ethAddr := ethCrypto.PubkeyToAddress(ethSk.PublicKey)
+
+	// BabyJubJub key
+	var sk babyjub.PrivateKey
+	_, err = hex.Decode(sk[:], []byte("0001020304050607080900010203040506070809000102030405060708090001"))
+	assert.NoError(t, err)
+
+	chainID := uint16(0)
+	hermezContractAddr := ethCommon.HexToAddress("0xc344E203a046Da13b0B4467EB7B3629D0C99F6E6")
+	a := AccountCreationAuth{
+		EthAddr: ethAddr,
+		BJJ:     sk.Public().Compress(),
+	}
+	msg, err := a.HashToSign(chainID, hermezContractAddr)
+	assert.NoError(t, err)
+	assert.Equal(t, "cb5a7e44329ff430c81fec49fb2ac6741f02d5ec96cbcb618a6991f0a9c80ffd", hex.EncodeToString(msg))
+
+	// sign AccountCreationAuth with eth key
+	sig, err := ethCrypto.Sign(msg, ethSk)
+	assert.NoError(t, err)
+	a.Signature = sig
+
+	assert.True(t, a.VerifySignature(chainID, hermezContractAddr))
+}